There is a distinction and sometimes it's overlooked. I don't think that the two rounds should be grouped in the same listing because although 5.56 weapons can shoot .223 just fine, 5.56 should not be fired in a .223 weapon. I used to own an older Mini-14 which was chambered for .223 only. Sometimes ammo retailers (online and LGS) are selling 5.56 ammo but labeling it "223 ammo" but it really isn't. When I bought that rifle the guy at the gun store told me to be careful about this issue. I shot tons or reloads through it that were labeled as .223 but they were from used brass from Ft. Benning which we know is 5.56. Nothing bad happened thank goodness. Just as frustrating is having a 5.56 gun and finding the 5.56 ammo you just bought was .223.